476 BULLETIN 188, UNITED STATES NATIONAL MUSEUM 



author in 1926, found they differed from Neostethus in having no 

 toxactinium and in other characters, and described them as represent- 

 ing a new genus and a new species under the present name. From 

 the account as already published (Smith, 1929), the following notes 

 are taken in part: 



The species abounds in fresh-watex- pools, ditches, and smaller canals in the 

 Bangkok region, living in water that is nearly always muddy or turbid. It occurs 

 in small, scattered schools that normally remain at or close to the surface, and 

 subsists on planktonic microorganisms. Small numbers put in balanced aquaria 

 did well for a time but ultimately died from starvation as the food supply became 

 exhausted. By the daily introduction of raw ditch or canal water, fish in 

 aquarium jars were kept alive for a month and could doubtless have been sus- 

 tained much longer. The larvae of anopheline mosquitoes, which are the chief 

 food of most of the small fresh-water fishes of the area, are entirely too large 

 for this fish to ingest, but there is no difficulty in taking minute crustaceans, 

 protozoau,s, worms, and similar organisms, which swarm in these waters. 



The color of the back harmonizes with the water in which the fish live, and 

 they would be diflacult to see when at or near the surface veere it not for a 

 glistening yellovp area on the top of the head ; this is of triangular shape, with 

 its apex on the nape. Viewed from the side the fish is transparent, the heart 

 and abdominal viscera are distinctly visible, the vertebrae may easily be counted, 

 and the presence of eggs is readily made out. 



The maximum total length of specimens measured was 20 mm., with the 

 females averaging slightly larger than the males. In one lot of 108 adult fish 

 comprising 46 males and 62 females, the largest number of males (28) measured 



18 mm. and none of them 20 mm., the largest number of females (30) measured 



19 mm. and 10 measured 20 mm. ; the average for males was 17.8 and for females 

 18.7 mm. 



It was not possible to make observations on spawning habits. The species 

 is oviparous, and the toxactinium and ctenactinium are undoubtedly used as 

 clasping organs to insure fertilization of the eggs as they are laid in the muddy 

 water. The egg-bearing and spawning periods are protracted, corresponding with 

 the rainy season and subsequent high water in river canals, and may extend 

 from May to December. Fish with enlarged ovaries were observed in July; 

 young 9 mm. long were collected in September and 10 to 12 mm. long in Novem- 

 ber; and eggs approaching maturity and numbering 67 were dissected from a 

 full-sized fish in November. 



The discovery in this species of a short, highly refractive spine, with 

 attached membrane, situated a short distance before the soft dorsal fin 

 raised the question of the systematic position of the Phallostethidae, 

 following the finding of a similar structure in Regan's material for 

 Neostethus in the British Museum, and led to the generally accepted 

 allocation of this family with the Percomorphi. 



The species called Phenacostethus thai by Fowler (1937) based on 

 specimens sent by the writer from Bangkok, can hardly be other than 

 the present species. The differences from the original description are 

 such, as Fowler himself suggested, as might arise from changes caused 

 by preservation. 



